Module 11: Collections Framework in Practice

Mini-Project: Contact Manager

Build a contact manager that combines lists, maps, and sorting in one small program.

Author

Java Learner Editorial Team

Reviewer

Technical review by Java Learner

Last reviewed

2026-04-17

Java version

Java 25 LTS

How this lesson was prepared: AI-assisted draft, manually edited for clarity, and checked against current Java documentation and runnable examples.

Learning goals

Project goal: Store contacts, prevent duplicate tags, look up by ID, and print sorted views by name or city.

Suggested collection choices: A map for ID lookup, a set for unique tags, and a list when you need ordered display output.

What to practice: Adding, updating, searching, sorting, and converting between collection types when needed.

Success check: Your chosen collection types should match the job instead of all data being shoved into one giant list.

Runnable examples

A map handles direct contact lookup

java.util.Map<Integer, String> contacts = new java.util.HashMap<>();
contacts.put(1, "Ada Lovelace");
System.out.println(contacts.get(1));

Expected output

Ada Lovelace

Mini exercise

Start with ID lookup and unique tags first, then add sorted output afterward.

Summary

Good collection design follows the access pattern.
One project can legitimately use several collection types together.
This module is about choosing structures intentionally, not memorizing every API method.

Next step

Next comes generics, which make collection-heavy code safer and more reusable.

Sources used